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What is "holing a piston"?

  • Thread starter Thread starter Anonymous
  • Start date Start date
A

Anonymous

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What is "holing a piston"?
Would someone give some details?

Thanks
 
If your burn is running too hot, you can melt a hole right through the top of the piston. Causes of this can be a poor fuel mixture, a bad exhaust or valves with too tight of a clearance. Your temp gauge (if you have one) most likely won't let you know. Keep an eye on those plugs!
 
Jethro said:
If your burn is running too hot, you can melt a hole right through the top of the piston. . Keep an eye on those plugs!
Click to expand...

WATCH OUT FOR WHITE PLUGS!

They mean you are running too lean, and that means you are running too hot.
 
Four strokes rarely have this problem because the extra intake and exhaust stroke transfer heat in between ignitions. It is much more prevalent in 2 strokes.
 
Don Lobacz said:
Four strokes rarely have this problem because the extra intake and exhaust stroke transfer heat in between ignitions. It is much more prevalent in 2 strokes.
Click to expand...

I can actually say that I have never seen this happen on a four stroke bike engine.
I have seen it a number of times on two strokes usually on bikes that I was running in scrambles. Usually I had problems like this running at high altitudes after jetting for a rainy morning start that turned into a hot dry afternoon and not taking the time to rejet. I did have one street bike do it, it was a Suzuki 305 scrambler (the last update of the X-6 high pipe model) it did it due to a crack in the cylinder.



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Keep in mind that we're talking about high combustion temps, not necessarily oil temps.

Basically, holing a piston happens when the combustion temps are too high, causing the aluminum on top of the piston to get weak. Eventually, a chunk of hot aluminum breaks out from the area suffering from the highest temps, and, well, it's not pretty after that.

Needless to say, there's usually damage to the cylinder bore, head, and valves from all the chunks of hot metal bouncing around. Quite often, there's also damage to the bottom end and bearings from smaller pieces making their way into the crankcase.

Before catastrophic failure, the rest of the piston is also getting far too hot and trying to expand too much, leading to warping, scoring, and bits of scraped off aluminum all over the place. Also not good.

You may see some tiny bits of melted aluminum, but most of the missing chunks of aluminum don't actually melt -- aluminum just gets very weak and breaks apart easily when it gets too hot.

So don't run lean. White spark plugs are bad, mmkaay?
 
I can actually say that I have never seen this happen on a four stroke bike engine.
Click to expand...

The more likely thing to happen on a four stroke bike is burning the exhaust side cam seats. A lean condiditon can cause these to get even hotter than they usually do. I melted a head on my 81 that way, but the pistons were just fine!
 
Jethro said:
The more likely thing to happen on a four stroke bike is burning the exhaust side cam seats. A lean condiditon can cause these to get even hotter than they usually do. I melted a head on my 81 that way, but the pistons were just fine!
Click to expand...

I melted miniature canyons into the middle two exhaust valves on my GS850 due to a lean condition caused by bad intake boot o-rings. The valve seats were actually OK, somehow.

So yes, you are more likely to burn a valve than hole a piston. Especially if you just keep riding the durn thing when it's running badly and you can't figure out why... :roll: (I was so young and foolish then...)

The pistons were pretty much OK, but those two pistons did show more wear from getting too hot.

One thing I forgot to mention before is that the shock waves from preignition (knocking) are usually the death blow for weakened, overheated pistons. If it's too hot in the combustion chamber, some bit of glowing carbon or whatnot can ignite the mixture prematurely and/or unevenly.
 
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